Fastlane DMA addressing emulation update.

diff --git a/ncr9x_scsi.cpp b/ncr9x_scsi.cpp
index 458c6281f6243a798f29be1071790c29aad6fc2f..25ffcfd6edbf678b280a4a62aa18a328f396e554 100644 (file)
--- a/ncr9x_scsi.cpp
+++ b/ncr9x_scsi.cpp
@@ -94,6 +94,7 @@ struct ncr9x_state
        uae_u32 expamem_lo;
        bool enabled;
        int rom_start, rom_end, rom_offset;
+       bool rom_bypass_if_write;
        int io_start, io_end;
        addrbank *bank;
        bool chipirq, boardirq, boardirqlatch;
@@ -1032,11 +1033,13 @@ static void ncr9x_io_bput3(struct ncr9x_state *ncr, uaecptr addr, uae_u32 val, i
                        }
                        return;
                } else if (addr < 0x01000000) {
-                       addr &= 3;
-                       addr = 3 - addr;
-                       ncr->dma_ptr &= ~(0xff << (addr * 8));
-                       ncr->dma_ptr |= (val & 0xff) << (addr * 8);
+                       // DMA address bits  0 to 23 comes from address bus.
+                       // DMA address bits 24 to 31 comes from data bus.
                        ncr->dma_cnt--;
+                       if (ncr->dma_cnt == 3) {
+                               ncr->dma_ptr = val << 24;
+                               ncr->dma_ptr |= addr;
+                       }
                        if (ncr->dma_cnt == 0 && (ncr->states[0] & FLSC_PB_ENABLE_DMA))
                                esp_dma_enable(ncr->devobject.lsistate, 1);
                        return;
@@ -1637,7 +1640,7 @@ static void ncr9x_bput2(struct ncr9x_state *ncr, uaecptr addr, uae_u32 val)
 #endif
 
        addr &= ncr->board_mask;
-       if (ncr->rom && addr >= ncr->rom_start && addr < ncr->rom_end) {
+       if (ncr->rom && addr >= ncr->rom_start && addr < ncr->rom_end && !ncr->rom_bypass_if_write) {
                if (addr < ncr->io_start || (!ncr->romisoddonly && !ncr->romisevenonly) || (ncr->romisoddonly && (addr & 1)) || (ncr->romisevenonly && !(addr & 1))) {
                        write_rombyte(ncr, addr, val);
                        return;
@@ -2034,6 +2037,7 @@ bool ncr_fastlane_autoconfig_init(struct autoconfig_info *aci)
        memcpy(ncr->acmemory, aci->autoconfig_raw, sizeof ncr->acmemory);
        ncr->rom_start = 0x800;
        ncr->rom_offset = 0;
+       ncr->rom_bypass_if_write = true; // DMA pointer set can write to ROM space
        ncr->rom_end = FASTLANE_ROM_SIZE * 4;
        ncr->io_start = 0;
        ncr->io_end = 0;